Improving the Performance of ZnO Thin-Film Transistors with ZnON Source/Drain Contacts

Motivation to study the ZnO channel for thin-film transistors (TFTs) is strong in light of its decent high mobility and large bandgap, enabling simultaneous coexistence of high on current and low off-state leakage. Nevertheless, the improvement in device performance for ZnO TFTs has not been fully exercised and even the field-effect mobility (μ
_FE
) is degraded with downscaling the channel length owing to considerable series source/drain (S/D) resistance (R
_SD
). In this paper, we show that inserting a thin contact layer of ZnON between the ZnO channel and Al S/D effectively suppresses the formation of interfacial layer of AlO
_x
and thereby reduces R
_SD
dramatically. This is evidenced by a significant reduction in R
_SD
from 30.1 to 14.4 kQ · μm measured on 0.5-μm ZnO TFTs with a ZnON contact layer or not, leading to an improvement in μ
_FE
from 18.2 to 29.6 cm
²
/V · s.